Recently, optical cables are increasingly installed in sewer pipes. And optical cable closure used for interconnection of optical cables are often installed along upper walls of manholes.
An optical cable closure of the prior art used for such a purpose as described above comprises a two-partition type outer casing 1 wherein a chamber 2 is formed by joining half cases 1A and 1B to face each other as shown in FIG. 8, while the outer casing 1 has a plurality of cable leading holes 4 provided on only one end thereof for introducing end portions of optical cables 3 to be connected, with the cable leading holes 4 being arranged side by side and divided into halves by a partition plane 5 of the outer casing 1. Plugged into each of the cable leading holes 4 and supported therein is an end plate 6 made of rubber having a circular cross section which fits around the circumference of the optical cable 3 and seals the cable leading hole 4. Housed in the chamber 2 of the outer casing 1 are a linkage frame 7, which holds the optical cable 3 and supports a reinforcement member of the optical cable 3, and a redundancy housing case 9 which houses a connecting portion and a redundant portion of optical fiber ribbon 8 of the optical cable 3.
The end plate 6 has a cable passing hole 6a made along the center line thereof and flanges 6b and 6c provided around the circumference at both ends in the direction of the center line, and the end plate 6 is, with a sealing tape 10 wound around the circumference between the flanges 6b and 6c, plugged into the cable leading hole 4 thereby sealing the cable leading hole 4.
Since the cable passing hole 6a of the end plate 6 is provided along the center line of the end plate 6, the end portion of the optical cable 3 is disposed along the partition plane 5 in the chamber 2 of the outer casing 1 as shown in the drawing. The end portion of the optical cable 3 comprises a cable spacer 12 exposed at the end of a sheath 11 and a reinforcement member consisting of a tension member 13 exposed at the end of the cable spacer 12. The cable spacer 12 has a plurality of grooves, which are not shown in the drawing, opening along the longitudinal direction around the circumference thereof, with the optical fiber ribbons 8 being housed in the grooves.
The linkage frame 7 is used for holding the end portion of the optical cable 3 in the chamber 2 and for holding the tension member 13 which is the reinforcement member of the optical cable 3, and has a shape of a bottomed box disposed in the chamber 2A of the half case 1A on one side of the outer casing 1. A cable holder 14 is provided on an upper edge 7a of one end of the linkage frame 7 for holding the optical cable 3, and a reinforcement member holder 15 is provided on an upper edge 7b of the other end for holding the reinforcement member consisting of the tension member 13. Since the end portion of the optical cable 3 is positioned along the partition plane 5, the cable holder 14 and the reinforcement member holder 15 are also provided along the partition plane 5.
Numeral 16 denotes a reinforcement holder fastened onto the linkage frame 7 with screws or the like for holding a metal tube inserted in a holding slit 16a, where in case the optical cable 3 is not provided with the tension member 13 and the slotted cable spacer 12 shown in the drawing, the optical fiber ribbon is housed in the metal tube serving as a reinforcement member instead.
In the chamber 2B of the half case 1B on the opposite side of the outer casing 1, a plurality of redundancy housing cases 9 are stacked for housing connecting portions and redundant portions of the optical fiber ribbons 8. The redundancy housing cases 9 are stacked and supported on a swingable support plate 17 which is placed on the box-shaped linkage frame 7 to span thereover and is pivoted on one side thereof onto the linkage frame 7 to freely open or close.